Skin-oil free electrostatic fingerprinting



Dec. 22, 1970 v v BRQDIE 3,549,253

SKIN-OIL FREE ELECTROSTATIC FINGERPRINTING Original Filed Oct. 11. 1966 SIGNATURE ADDRESS RIGHT RIGHT RIGHT RIGHT RIGHT THUMB INDEX MIDDLE RING LITTLE LEFT LEFT LEFT LEFT LEFT THUMB INDEX MIDDLE RING LITTLE Q ,J INVENTOR W VOR BRODIE LEFT FouR FINGERS LEFT RIGHT RIGHT FOUR BY THUMETHUMB FINGERS X I TORNEY United States Patent O 3,549,253 SKIN-OIL FREE ELECTROSTATIC FINGERPRINTING Ivor Brodie, Palo Alto, Calif., assignor to Varian Associates, Palo Alto, Calif., a corporation of California Continuation of application Ser. No. 585,913, Oct. 11, 1966. This application Nov. 10, 1969, Ser. No. 871,567 Int. Cl. G03g 9/04 US. Cl. 355 6 Claims ABSTRACT OF THE DISCLOSURE This is a continuation of application Ser. No. 585,913, filed Oct. 11, 1966, now abandoned.

The present invention relates in general to fingerprinting and, more particularly, to an improved method and apparatus for fingerprinting wherein electrostatic fingerprint images are layed down on a recording web for subsequent development by preferably a liquid toner, whereby the imaging and development functional steps are separated to avoid inking the fingers in the process. Such improved fingerprinting means are especially suitable for obtaining permanent fingerprints of persons that would otherwise object to the messy prior art inking process. In addition, the speed with which the prints can be taken is substantially increased.

Heretofore, the conventional fingerprinting method required that the hands and fingers be thoroughly cleaned, that printers ink be evenly distributed by a roller onto an inking slab, and that the ink be transferred from the slab to the fingers and thence to the pre-printed form on which the fingerprints were to be recorded. As most persons can verify by their own experience the ink remaining on the fingers after the printing is messy and difficult to remove.

In the present invention, a writing potential, as of 100 to 500 volts from a very high impedance source, is applied between the fingers and the back side of a dielectrically coated slightly conductive paper. The fingers with the potential applied are pressed against the dielectric surface of the paper. In the process, a latent electrostatic fingerprint image is deposited on the dielectric surface of the paper. This latent image is then developed by applying a liquid toner to the image. Upon drying of the paper, which can be accomplished with a few seconds, there is produced a permanent, faithful, high resolution fingerprint image.

The advantages of this system are that the persons fingers never come in contact with the ink and, therefore, the method is clean. Secondly, no elaborate preparations such as cleaning of the hands nor preparation of the inking slab are required. Therefore, the speed with which fingerprints can be taken can be substantially increased.

Although an electrical potential is applied between the fingers and the paper on which the prints are recorded, the current required for the electrostatic printing is only on the order of a microamp or less and there is no danger to the person, nor is there any detectable electrical sensation involved in the process.

The principal object of the present invention is the provision of an improved method and apparatus for making prints or portions of a persons extremities (fingerprinting).

One feature of the present invention is the provision of method and apparatus for fingerprinting wherein a writing electric potential is applied between a persons extremity such as a finger, hand, foot or other portion to be printed and a dielectric recording medium, such that when that portion of the person, which is to be printed, is brought into contact with or into close proximity to the recording medium a latent charge image thereof is caused to be deposited on the recording medium. This charge image may then be subsequently developed, whereby such prints are obtained without ink having to come into contact with the person being fingerprinted.

Another feature of the present invention is the same as the preceding feature wherein the electrostatic image is rendered visible by application of pigment particles colloidally suspended in a dielectric liquid, whereby oil transferred from the persons skin to the recording medium does not serve to hold pigment particles or to otherwise interfere with a proper development of the latent charge image.

Another feature of the present invention is the same as any one or more of the preceding features wherein the recording medium comprises a dielectric film on a slightly electrically conductive paper web, whereby the image is developed directly upon the Web, forming a permanent record.

Another feature of the present invention is the provision of a fingerprint form comprising a printed format on a recording web having blank spaces for the persons name and other data and including marked off regions with finger identifving indicia for recording the fingerprints, such marked oft regions formed by a condurtive backing portion of the web having a dielectric overlay for receiving electrostatic images of the fingerprints for subsequent development, whereby the fingerprints are recorded without ink having to come into contact with the persons skin.

Other features and advantages of the present invention will become apparent upon a perusual of the following specification taken in connection with the accompanying darwings wherein:

FIG. 1 is a perspective schematic view, partly broken away, of an electrostatic fingerprinting apparatus of the present invention, and

FIG. 2 is a plan view of a fingerprinting form incorporating features of the present invention.

Referring now to FIG. 1 there is shown a fingerprinting machine 1 of the present invention. The machine 1 includes a supply roll of electrographic recording Web 2. A suitable Web 2 is electrographic paper marketed by Crown Zellerbach and Plastic Coating Corporation and comprising a slightly conductive paper backing with a thin dielectric film on one side thereof forming the recording surface.

In a preferred embodiment of the present invention, the dielectric surface of the web 2 is pre-printed with a suitable format as depicted in FIG. 2. Such format including blank lines 3 for the persons name and other pertinent data and including a plurality of marked off regions 4 each marked with printed indicia identifying the particular fingerprint to be recorded in each of the marked off regions 4.

The printed recording web 2 is threaded through a system of rollers and out through a slot 5 in the top of a sheet metal housing 6 Which contains the web 2 and the system of rollers. The system of rollers includes a first idler roller 7 near the front of the cabinet 6 over which.

the web 2 passes. Thence, the web 2 is passed over a plate electrode 8 and around a second idler roller 9 to a pair of friction drive rollers 11 and 12. One of the drive rollers 11 is coupled to a knob 13 or crank disposed externally of the cabinet 6 for cranking the web 2- through the machine 1 and out the slot 5. The other drive roller 12 is an idler roller which is spring loaded to provide a friction force between the drive roller 11 and the web 2.

The front of the cabinet 6 is provided with an outwardly projecting tongue portion 14 which is relatively thin such that it may be readily gripped between the fingers and thumb of a persons hand. A rectangular opening 15 is provided near the forward edge of the tongue 14 and over the plate electrode 8. A window 16 is placed in the tongue 14 such that the operator may see through to the printed format on the web 2 for properly positioning the fingerprint regions 4 of the form in registration with the opening 15.

A positive potential, as of +100 to +500 volts, is applied to the plate electrode 8 from a voltage supply 17 through a high resistance 18 as of lOMSl. The conductive paper side of the web 2 is in contact with the electrode plate 8. The person being fingerprinted graps the tongue 14 and presses each finger successively into each of the regions 4 of the printed form on the web 2. As the finger is pressed against the dielectric recording surface of the web 2 an electrical circuit is completed from the grounded cabinet 6, forming one electrode in electrical contact with the persons skin, through the web 2, plate 8, resistance 18 to the voltage supply 17. Under these conditions, a negative charge image of the fingerprint is formed on the dielectric surface of the web 2. The web 2 is then advanced and additional prints taken of the other hand. When the persons fingerprints are all taken, the web 2 is cranked by crank 13 such that the imaged side of the web 2 is caused to pass an inker 19 disposed adjacent the web 2 between the drive rollers 11 and 12 and the idler roller 9.

The inker 19 comprises a hollow elongated inking channel 20 extending laterally of the web 2. An inking slot 21 is cut through the side of the channel facing the web 2. A liquid electrographic toner (ink) is fed into the inking channel 20 at one end from a reservoir, not shown. A pump, not shown, is connected to the other end of the channel to pull ink through the channel from the reservoir at less than atmospheric pressure. The reduced pressure on the inking slot 21 causes the atmospheric pressure to push the web 2 up against the marginal edges of the slot 21 sealing same and bringing the electrostatic image into contact with the liquid ink. As a consequence, the positively charged colloidally suspended pigment particles of the ink are pulled out of suspension and electrostatically bound essentially only to the charge image portion of the web 2, thereby developing a visible image thereof.

A suitable liquid ink is a mixture of /2% to 4% by volume of liquid toner concentrate in Shell Chemical Companys No. 72 solvent, which is dielectric. The toner concentrate is marketed by Philip A. Hunt Company.

The imaged web 2 may be cranked or pulled through the inker 19 at any convenient speed from a few inches per hour to inches per second. The liquid inking channel 19, which is operated at less than atmospheric pressure, is particularly advantageous as the solvent portion of the ink dissolves or otherwise prevents pigment particles from being bound to skin oil images placed by the fingers upon the web 2 during the finger printing process. It has been found, when using a conventional dry powder development of the latent electrostatic fingerprint images, that the oil images are also developed and interfere with the proper development of the electrostatic images. Thus, if a conventional powder development is employed, the oil images should first be removed by a suitable dielectric solvent that will not disturb the latent electrostatic image.

In addition, the marginal edges of the inking slot 21 perform a sort of squeegee action causing the developed web 2 to emerge from the slot in a nearly dry condition. Drying is complete within a minute or so depending upon the quick drying nature of the solvent used in the liquid 4 ink. Upon drying, the developed image is fixed without further treatment.

The web 2 is cranked or pulled through the slot 5 and the printed forms separated by tearing the web across a cutting edge 22 disposed adjacent the slot 5.

Although the fingerprinting machine 1 has been described using a continuous strip of recording web 2, this is not a requirement and individual cards formed of the electrographic paper may be used as well. In such a case the cards could be pre-printed with the desired format and placed in a machine which is essentially only the tongue portion 14 of the machine of FIG. 1 for depositing the electrostatic prints upon the card. The card could then be removed and inserted into an electrographic inker similar to that portion of the machine of FIG. 1 including the rollers 11 and 12 and the inking channel 19.

Alternatively, the liquid ink may be applied to the web by a brush, roller, areosol spray can or by dipping. Moreover, the method and apparatus of the present invention is useful for taking prints of other extremities of a person such as footprints.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim: 1. The method for making recorded prints of a persons extremities without adverse effects caused by oils of the human skin, comprising the steps of:

placing a portion of the persons extremity to be printed adjacent a dielectric surface of a recording medium;

applying an electrical potential between the persons extremity and the recording medium to cause a transfer of electrical charge to the dielectric surface to form a latent electrostatic charge image of the to be printed portion of the persons extremity on the dielectric surface, and

developing the charge image to produce a visible print of the image by applying a colloidal suspension of pigment particles in a dielectric solvent for the oils of the human skin causing the charged pigment particles in the suspension to be attracted out of the suspension and electrostatically bound substantially only to the charge image and causing any image of the skin oil to be substantially dissolved into the dielectric solvent.

2. An electrostatic printing apparatus for making skin oil free prints of portions of persons extremities on a recording medium comprising:

a dielectric recording medium;

means for applying an electrical potential between a portion of a persons extremity to be printed and the recording medium when the persons extremity is disposed adjacent the recording surface of the recording medium for causing a transfer of electric charge to the recording surface to form an electrical charge image thereon;

means for applying a colloidal suspension of pigment particles in a dielectric liquid to the charge image for rendering a visible print of the charge image; and

a solvent for human skin oil contained in the dielectric liquid for substantially dissolving any skin oil image deposited on the recording medium while the persons extremity was placed adjacent thereto.

3. The apparatus of claim 2 wherein said means for applying an electrical potential between the person and the recording medium includes an electrode against which the recording medium is pressed by that portion of the extremity to be printed.

4. The apparatus of claim 3 wherein said means for applying an electrical potential between the person and the recording medium further includes a second electrode operated at a potential diflerence relative to said first electrode and which second electrode makes electrical connection to the skin of the person.

5. The apparatus of claim 2 including in combination, means forming a web constituting the recording medium, said web having a dielectric surface constituting the recording surface onto which is deposited the charge image to be developed.

6. The apparatus of claim 5 wherein said recording 1 web further includes an electrically conductive backing portion onto which is formed said dielectric recording surface as a composite portion thereof.

References Cited UNITED STATES PATENTS 1,206,362 11/1916 Parliman 117.5UX 3,408,217 10/1968 Obuchi 117-.5

JOHN M. HORAN, Primary Examiner R. P. GREINER, Assistant Examiner US. Cl. X.R. 

